Post on 17-Sep-2015
description
Geo-Referencing & Geo-Coding
Contents Geo-referencing
Need for Geo-referencing
Types of Geo-referencing
Methods
Steps for Geo-referencing
Geo-coding
Difference between the two
Geo-referencing for digitization
Geo-ReferencingGeo-referencing is the process of scaling, rotating, translating and
de-skewing the image to match a particular size and position
To Georeference means to associate something with locationsin physical space.
The term is commonly used in the geographic informationsystems field to describe the process of associating a physicalmap or raster image of a map with spatial locations
Georeferencing may be applied to any kind of object orstructure that can be related to a geographical location, such aspoints of interest, roads, places, bridges, or buildings
Need for Geo-referencingGeo-reference is used when establishing the relation between raster
or vector images by determining the spatial location of thegeographical features
This procedure is mandatory for data modeling in the field ofgeographic information systems (GIS)
When data from different sources or time periods (like time seriessatellite images) need to be combined and then used in a GISapplication, (e.g. for change detection, assess damages after anatural disaster etc.), it becomes essential to have a commonreferencing system
Types of Geo-referencingTwo types:
1.Geo-referencing Raster Images
2.Geo-referencing Vector Data
Geo-referencing Raster Images A crucial element of any mapping project is registering a map with the correct
real world coordinates. This procedure is called geo-referencing. If the mapsare not geo-referenced, no other information can be displayed over orpositioned under the map coverage.
Depending on the source materials and the specifications of the project, mapscan be registered to either a coordinate system or to another base map such asa digital ortho photo.
Geo-referencing Vector Data
Vector data can be geo-referenced (or rubber sheeted) toreal world coordinates. Vector data can be either rubbersheeted to match existing base maps or the data may beprojected into a specific coordinate system.
Geo-Coding Geocoding is the conversion of Geo-refencing (spatial information)
into digital form
Geocoding involves capturing the map, and sometimes also capturing the attributes
Assigning spatial coordinates to point data
Geocoding Methods for Maps Digitizing
Scanning
Field Data Collection
Vector and Raster In ArcView Feature Data Source, Image Data Source
Often involves address matching
Difference between the twoGeo-referencing: Matching geographic images tocoordinates
Geo-coding: Matching addresses to geographic coordinates(latitude & longitude)
Geo-referencing for DigitizationWhat is digitization?Capturing data by converting features on a paper map or (digital) aerialphotograph into digital vector format
Methods
Method Devices
Manual digitising Coordinate entry via keyboard Digitising tablet with cursor Mouse cursor on the computer
monitor: on screen digitising (heads-up) Digital photogrammetry
Automatic digitising Scanner
Semi-automatic digitising
Scanner and line-following software
The image is a photo of the 3D model
Georeferencing: What to do?
Data are not yet structured into classified and coded objects
Image data has to be vectorised and structured first
ConclusionUsed to convert the entire map onto a real-world co-ordinate system
With Georeferencing you can align geographic data to a known coordinatesystem so it can be viewed, queried, and analyzed with other geographic data
Geocoding is a GIS operation for converting street addresses into spatial datathat can be displayed as features on a map, usually by referencing addressinformation from a street segment data layer